If you've had the phone a while I'm surprised you survived this long on MDC. MDL is still one update away from the current version. You might as well go to the Software update menu and download the final update to MF9. At that point make sure you back up your personal files or have sync enabled for the proper items. Many users have to factory reset after the update to clean out some software issues.

From there, you can use QBKing's site and video (see sig) to root MF9.

My wife and I got the update notices the minute the phones came out of the boxes back in August. Either way, you should go ahead and have the phone finish installing all the updates necessary before going further.

Your phone must be on a slow provisioning list to just get MDL but not pick up MF9 yet which was released in July. Give this a try first: QbKing77 | Your Tech Simplified, then bounce through his site for the MF9 root tutorial.

Which part gave you that error? Upgrading the firmware manually or rooting?

Hopefully you were able to pull that off successfully. The phone has built in security that does not like downgrades and some people have lost their phones in the process. Once this security feature is tripped, it locks your phone into an unsalvageable brick.